1. Field of the Invention
This invention relates to coating compositions, particularly to coating compositions containing aluminum flake, more particularly to an improvement in these coating compositions.
2. Prior Art
Pollution problems caused by conventional paints which utilize organic solvents are forcing the manufacturing industries, such as the automobile and truck manufacturing industries, to turn to
(1) dry powder coating compositions, PA1 (2) water-based coating compositions that contain only small amounts of organic solvents, or PA1 (3) high solids coating compositions, i.e., a composition that contains very little, if any, liquid carrier.
Aluminum flake has been utilized in conventional solvent-based coating compositions to provide high quality finishes with an exceptional glamor appearance. "Glamor" is a term used in the coating art to indicate that property of a metallic pigmented coating which causes the intensity of light reflected from the coated substrate to vary markedly according to the angle from which it is observed, as well as, providing sparkle and an illusion of depth in the coating. However, standard, i.e., untreated aluminum flake, provides poor glamor appearance in dry powder and high solids coating compositions, and is unstable in water-based coating compositions.
When standard aluminum flake is added to a dry powder coating composition, the coating prepared is usually poor in appearance and exhibits a salt and pepper effect due to ineffective mixing. Additionally, in both dry powder and high solids coating compositions, any incompatible material will float to the surface. This diminishes the glamor effect. In those coatings where the flake is not properly aligned, it will also break through the surface of the coating.
In water-based coating compositions, standard aluminum flake will both react with water in the composition to form hydrogen gas, particularly at elevated temperatures, creating a safety hazard, and tend to settle to form a hard cake in the water-based coating composition.
The improved coating composition of this invention overcomes these aforementioned problems of the art.